1. Field of the Invention
The present invention relates to surface mount type piezoelectric vibrator, oscillator, electronic device, and radio clock. For example, the present invention relates to an electronic device using a surface mount type piezoelectric vibrator or the like, an external electrode of which is composed of an alloy metal of chrome and nickel and which can be soldered again.
2. Description of the Related Art
As an electronic element indispensable for manufacture of an industrial product, there is a quartz crystal vibrator in which a quartz crystal vibrator piece is encapsulated in an airtight container.
A quartz crystal has a property that it expands and contracts due to a piezoelectric effect when a voltage is applied thereto. If the quartz crystal is incorporated in a feedback circuit of a resonance circuit, it carries out very accurate and stable oscillation.
By using this property, a quartz crystal vibrator is used for all electronic products including an electronic device such as a vibrator, an information and communication device, a mobile device, and a home appliance or the like as a clock function and frequency control mechanism.
As a quartz crystal vibrator, there is one of a lead type in which a lead wire is arranged and one of a surface mount type in which a package is directly mounted on a printed board or the like.
FIG. 8A is a conceptual illustration showing a section in a longitudinal direction of a quartz crystal vibrator of a conventional surface mount type. A surface on which an external electrode 110 and an external electrode 111 are formed is a face contacting a printed board.
A quartz crystal vibrator 101 is composed of a lid 102 that is made of a glass member represented by a soda lime glass, a base 103, exciting electrodes 105 and 106 that are made of aluminum or the like, and a quartz crystal vibrator piece 107 or the like.
The exciting electrodes 105 and 106 are formed on front and rear surfaces of the quartz crystal vibrator piece 107 and they are used to apply a voltage to the quartz crystal vibrator piece 107.
At the outer surfaces of the exciting electrodes 105 and 106, the lid 102 and the base 103 are pasted with anodic bonding (to be described in detail in the embodiment) to form a glass package.
On the lid 102 and the base 103, concave portions are formed and these concave portions form a cavity 104 in which the quartz crystal vibrator piece 107 oscillates.
In the vicinity of an end face of a bottom part of the base 103, the external electrode 110 and the external electrode 111 are formed. The external electrode 110 and the external electrode 111 are terminals to solder the glass package on a base.
Although it is not illustrated, the external electrode 110 is connected to the exciting electrode 105 and the external electrode 111 is connected to the exciting electrode 106. Then, if a voltage is applied to the external electrode 110 and the external electrode 111, the voltage is applied to the exciting electrode 105 and the exciting electrode 106, and the quartz crystal vibrator piece 107 can be driven.
FIG. 8B is an enlarged view of the external electrode 110.
The external electrode 110 is of two-layer structure including a base metal 115 formed on the base 103 and a surface metal 116 formed on the surface of the base metal 115.
The base metal 115 is made of Cr (chrome) and the surface metal is made of Au (gold).
The base metal 115 secures coherence to the glass and the surface metal 116 forms an alloy metal with solder. The structure of the external electrode 111 is the same.
In other words, since Cr sticks to the glass but is not an appropriate metal for soldering, Au that is bonded to Cr and can be soldered is formed on the surface of Cr.
In this way, for the art that relates to a surface mount type of quartz crystal vibrator, there is a method to manufacture a quartz crystal vibrator by the anodic bonding. As a result, the quartz crystal vibrator 101 as shown in FIGS. 8A and 8B is obtained.
There is a demand to detach the quartz crystal vibrator 101 that has been soldered once and solder it again, for example, a demand to conduct an experiment by transferring the same quartz crystal vibrator 101 to a plurality of electronic circuits or the like.
By the way, the surface metal 116 (namely, Au) is diffused in a solder by soldering once because Au has a high diffusion speed into the solder. On the other hand, Cr composing the base metal 115 does not form an alloy metal with the solder.
Therefore, it is difficult to detach the quartz crystal vibrator 101 that has been soldered once and solder it again.
In place of Cr, Ti (titan) may be used, however, Ti does not form the alloy metal with the solder in the same way.
In addition, not in a glass package but in a ceramics package in which an airtight container is constituted of ceramics, Ni (nickel) may be used for the external electrode. However, since Ni has a large stress of film, if this is used for the glass package, the glass may be damaged or the film of Ni may be peeled off.
In addition, if a film thickness of Ni is made thin in order to reduce the stress, Ni is diffused in the solder the same as Au, so that it is difficult to solder Ni again. Particularly, this phenomenon is remarkable in Pb (lead) free soldering.